精确计算n-n重正化链图传播下n+n→２π0反应截面

采用中子n-反中子n与中性介子π⁰强相互作用的Lorentz不变耦合模型,对n-n重正化链图传播子作了有关物理分析及其严格解析计算,获得精确理论计算结果. 进而将此结果用于n+n→2π⁰反应的物理过程分析及其截面的计算研究中,并精确计算出n-n重正化链图传播下n+n→2π⁰反应微分截面. 还将此计算结果与n-n树图和重正化单圈链图传播下n+n→2π⁰反应微分截面作了对比分析,获得了有关辐射修正的重要信息. 此结果对于深 关键词： Lorentz不变耦合模型 重正化链图传播子 微分截面 辐射修正     

一种精确求解三原子反应散射的传播子

The exact short time propagator, in a form similar to the Crank-Nicholson method but in the spirit of spectrally transformed Hamiltonian, was proposed to solve the triatomic reactive time-dependent schrödinger equation. This new propagator is exact and unconditionally convergent for calculating reactive scattering processes with large time step sizes. In order to improve the computational efficiency, the spectral difference method was applied. This resulted the Hamiltonian with elements confined in a narrow diagonal band. In contrast to our previous theoretical work, the discrete variable representation was applied and resulted in full Hamiltonian matrix. As examples, the collision energy-dependent probability of the triatomic H+H₂ and O+O₂ reaction are calculated. The numerical results demonstrate that this new propagator is numerically accurate and capable of propagating the wave packet with large time steps. However, the efficiency and accuracy of this new propagator strongly depend on the mathematical method for solving the involved linear equations and the choice of preconditioner.     

Path Integral for a Pair of Time-Dependent Coupled and Driven Oscillators

The propagator for a certain class of two time-dependent coupled and driven harmonic oscillators with time-varying angular frequencies and masses is evaluated by path integration. This is simply done through suitably chosen generalized canonical transformations and without presupposing the knownledge of any auxiliary equation. The time-dependent oscillators system with exponentially growing masses and coupling coefficient in time may be considered as a particular case.     

解析计算SM中电子混合链图传播下Compton散射微分截面(英文)

采用电弱统一标准模型（SM）,对由参与电弱相互作用的各种混合圈构成的电子重整化链图传播子的构架方式作了详细分析,并完成了有关解析计算,进而获得了电子重整化链图传播子的解析计算结果.作者又将此结果应用到Compton散射,精确计算了电子混合链图传播下Compton散射微分截面的解析结果dσ_SM^chain/dcosθ.此外,作者还将计算结果与最低阶微分截面dσ^trcc/dcosθ口和量子电动力学（QED）中电子链图传播下的Compton散射微分截面dσ_QED^chain/dcosθ做了具体的数值计算与对比分析,发现dσ_SM^chain/dcosθ比dσ_QED^chain/dcosθ能更加精细的反应辐射修正效应.     

Do Dyson Orbitals resemble canonical Hartree–Fock orbitals?

ABSTRACT

Dyson orbitals are overlaps between states with N and N±1 electrons and provide conceptual links between transition probabilities of electron detachment or attachment, density matrices, total energies and general principles of chemical bonding. Canonical, Hartree–Fock orbitals are compared with Dyson orbitals obtained with electron–propagator calculations that retain all elements of the self–energy matrix, wherein all orbital–relaxation and electron–correlation corrections to Koopmans results reside. For valence ionization energies and electron affinities of representative closed–shell molecules, canonical, Hartree–Fock orbitals usually are excellent approximations to Dyson orbitals, although there are some notable cases where the resemblance is not as strong. Numerical relationships between pole strengths and the Koopmans contributions to Dyson orbitals also are inferred from the data.     

数据采集方案对神经扩散模型影响的评估

基于单次数据采集的多种扩散模型联合应用已逐渐成为临床研究的热点,本研究比较了三种采集方案对于神经扩散模型定量计算的影响,包括Q空间笛卡尔网格（QGrid）、多壳层异向（Free）和多壳层同向（MDDW）采集方案,涉及的扩散模型包含扩散张量成像（DTI）;扩散峰度成像（DKI）;神经突方向分散度和密度成像（NODDI）;平均表观传播（MAP）模型.结果表明DTI和DKI模型对采集方案相对不敏感,而NODDI和MAP对采集方案和最大b值的设置相对较敏感,并且QGrid和Free方案一致性较高,因此在大样本和多中心研究中需要考虑采集方案的选择.此外,考虑到QGrid和Free方案分别在结合更多扩散模型和神经纤维束成像应用上更具优势,因此推荐使用.     

Nearfield acoustic holography in a moving medium based on particle velocity input using nonsingular propagator

Nearfield acoustic holography in a moving medium is a technique which is typically suitable for sound sources identification in a flow.In the process of sound field reconstruction,sound pressure is usually used as the input,but it may contain considerable background noise due to the interactions between microphones and flow moving at a high velocity.To avoid this problem,particle velocity is an alternative input,which can be obtained by using laser Doppler velocimetry in a non-intrusive way.However,there is a singular problem in the conventional propagator relating the particle velocity to the pressure,and it could lead to significant errors or even false results.In view of this,in this paper,nonsingular propagators are deduced to realize accurate reconstruction in both cases that the hologram is parallel to and perpendicular to the flow direction.The advantages of the proposed method are analyzed,and simulations are conducted to verify the validation.The results show that the method can overcome the singular problem effectively,and the reconstruction errors are at a low level for different flow velocities,frequencies,and signal-to-noise ratios.     

在同位旋SU(2)不变耦合模型中研究 p pbar -> n nbar 核子反应的重整化无穷阶链图效应

本文采用描述中性及荷电 pion 介子（pion0,pion+,pion-）与核子-反核子强相互作用的同位旋SU(2)不变耦合模型,计算出在pion0 及 pion+, pion- 重整化链图传播下 p pbar -> n nbar 核子反应微分截面的“精确”解析结果;并且将此结果与在 pion0 及 pion+, pion- 树图传播下的微分截面作了对比分析,得到相应的辐射修正重要信息。本文完成的工作对进一步深入研究三种荷电状态 pion 介子与核子-反核子强相互作用的同位旋SU(2)不变耦合模型以及深入理论探讨质子-反质子对撞实验,都将提供某些理论研究的参考价值。     

ILC上e~+e~-对撞产生t~+t~-夸克对

本文结合国际直线对撞机(ILC)的实验讨论了e+e-湮灭产生t+t-对过程.在具体计算过程中,本文采用一种新的计算方式,即"混合链图传播子"修正下的反应截面,首先对QED中Dyson链图传播子理论在电弱统一标准模型(WS)中做了推广,获得WS中的光子、中间玻色子混合链图传播子,进而计算了γ,Z0混合链图修正下e+e-→t+t-反应总截面σchain,并与单圈修正下的总截面σloop和最低阶总截面σ0做了对比分析,发现在国际直线对撞机对撞能区,σchain对σloop和σ0的修正很大.此外,作者还结合国际直线对撞机的对撞亮度,讨论了每年可在ILC上产生t+t-对的事例数.     

Semiclassical propagator and van Vleck determinant in a mixed position--momentum space

In this paper a semiclassical propagator in a mixed position--momentum space is derived in the formalism of Maslov's multi-dimensional semiclassical theory. The corresponding mixed van Vleck determinant is also given explicitly. The propagator can be used to locally fix semiclassical divergences in singular regions of configuration space. It is shown that when a semiclassical propagator is transformed from one representation to another, its form is invariant.